The invention relates to current-source inverter (CSI) induction motor drives, in general, and more particularly to control of such a motor drive for operation in the braking, or regenerative mode, as well as in the motoring mode.
It is known to operate a CSI motor drive in the braking, or regenerative mode, while measuring shaft speed in order to derive a slip signal which can be used to achieve full current regenerative mode operation. See for instance "Current-Source Converter for AC Motor Drives" by Kenneth P. Phillips on page 195 and FIG. 8 in Adjustable Speed AC Drive Systems/Bimal K. Bose IEEE Press 1981. The present invention allows such regenerative mode of operation without having to measure shaft speed.
It is known to transfer control to the regenerative mode without the use of a tachometer. The prior art methods, however, only allow the motor to regenerate at a current level which is roughly equal to the magnetization current of the motor. For full current regeneration, the prior art still required the use of a tachometer.
The object of the present invention is to achieve full current regeneration in a CSI motor drive without using a tachometer. Not only is a tachometer an additional cost, but a tachometer, that it be digital, or analog, would have to be interfaced through electronics for microcomputer control, which increases the cost and decreases reliability. The present invention leads to a simpler system design, in particular since only line current, motor voltage, and DC link voltage are sensed.